XOTcl– an Object-Oriented Scripting Language Gustaf Neumann Uwe Zdun Department of Information Systems Specification of Software Systems Vienna University of Economics University of Essen Vienna, Austria Essen, Germany [email protected] [email protected] First European Tcl/Tk User Meeting, 15/16th June 2000 XOTcl– an Object-Oriented Scripting Language June, 2000 Overview ◆ XOTcl = Extended Object Tcl ◆ XOTcl is freely available from: http://nestroy.wi-inf.uni-essen.de/xotcl ◆ Outline: – Scripting and object-orientation, – XOTcl high-level language constructs, – Example: design pattern-based design of an XML interpreter, – xoComm HTTP implementation: performance comparison with Apache. Gustaf Neumann, Uwe Zdun Slide 1 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Tcl-Strengths Important Ideas in Tcl: ◆ Fast & high-quality development through component-based approach ◆ 2 levels: “System Language” and “Glue Language” ◆ Flexibility through . – dynamic extensibility, – read/write introspection, – automatic type conversion. ◆ Component-Interface through Tcl-Commands ◆ Scripting language for glueing Gustaf Neumann, Uwe Zdun Slide 2 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Motivation for XOTcl ◆ Extend the Tcl-Ideas to the OO-level. ◆ Just “glueing” is not enough! Goals are . – Architectural support – Support for design patterns (e.g. adaptations, observers, facades, . ) – Support for composition (and decomposition) ◆ Provide flexibility rather than protection: – Introspection for all OO concepts – All object-class and class-class relationships are dynamically changeable – Structural (de)-composition through Dynamic Aggregation – Language support for high-level constructs through powerful interceptors (Filters and Per-Object Mixins) Gustaf Neumann, Uwe Zdun Slide 3 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Filters ◆ A filter is a special instance method registered for a class C. Every time an object of class C receives a message, the filter is invoked automatically. ◆ Three parts, each optional: Filter_3 – pre-part, filter-chain Filter_2 } Class A – call to next, invokes: Filter_1 filter-chain, Class A • actual called method. o pre-part • call a1 – post-part. post-part result ◆ Filter-inheritance. Gustaf Neumann, Uwe Zdun Slide 4 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Example: Simple Filter Class A ;# Class Definition A a1 ;# Instance a1 of A A instproc Filter-1 args { ;# Filter instance method puts "pre-part of Filter-1" next puts "post-part of Filter-1" } A filter Filter-1 ;# Filter registration a1 set x 1 ;# Method invocation Applications: Trace facility, Composite Pattern, Proxy Pattern, Observers . Gustaf Neumann, Uwe Zdun Slide 5 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Per-Object Mixins ◆ A per-object mixin is a class which is mixed into the precedence order of an object in front of the precedence order implied by the class hierarchy. Motivation: ◆ Model behavior of individual objects Object (decorator). ◆ Handle orthogonal aspects not only next through multiple inheritance. next next ◆ Intrinsic vs. extrinsic behavior, similar to roles. Mix1 A . proc1 proc1 proc2 per-object Applications: timing, statistics, persistence, mixin instance-of life-cycle, chain of responsibility, adapter method anObject invocation Gustaf Neumann, Uwe Zdun Slide 6 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Example Code for Per-Object Mixins Class A ;# Class definition A instproc proc1 {} { ;# Method definition puts [self class]; next } A instproc proc2 {} { ;# Method definition puts [self class]; next } Class Mix1 ;# Class definition Mix1 instproc proc1 {} { ;# Method definition puts [self class]; next } A anObject ;# Instantiation of class A anObject mixin Mix1 ;# Mixin registration anObject proc1 ;# -> results in output "::Mix1 ::A" anObject proc2 ;# -> results in output "::A" Gustaf Neumann, Uwe Zdun Slide 7 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Dynamic Object Aggregations and Nested Classes ◆ Nesting though namespaces: Classes and objects in XOTcl can contain other classes/objects. Dynamic Object Aggregation resembles Part-of relationship in a dynamic ! and introspective fashion. Nested Classes reduce interference of independently developed program ! structures. ◆ Class nesting and aggregation semantics are handled through XOTcl object system (including built-in methods for deep copy and deep move). Gustaf Neumann, Uwe Zdun Slide 8 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Example Code: Nested Classes/Dynamic Object Aggregation Class Agent ;# Class definition Class Agent::Head ;# Nested classes Class Agent::Body Agent instproc init args { ;# Constructor aggregates two ::Agent::Head [self]::head ;# objects dynamically ::Agent::Body [self]::body } Agent myAgent ;# Object creation puts "Children: [myAgent info children]" ;# Output: head body myAgent::head destroy ;# Agent looses his head puts "Children: [myAgent info children]" ;# Output: body Gustaf Neumann, Uwe Zdun Slide 9 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Further Functionalities provided in XOTcl ◆ Assertions reduce interface and reliability problems caused by dynamic typing: – Design by contract: invariants and pre-/post-conditions for methods, – per-class and object-specific assertions. ◆ Meta-Data enhances self-documentation of objects and classes. ◆ Automatic Name Creation with autoname. ◆ Abstract Classes, ◆ Parameters. Gustaf Neumann, Uwe Zdun Slide 10 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Example: XML Parser/Interpreter ◆ Constructs a composite object structure from XML documents ◆ OO-implementation using design patterns, based on TclXML, around 120 lines (including example visitors and reusable pattern) ◆ Changeability and Adaptability through: – dynamics, – introspection, – patterns in hot spots, – interceptors per-object and filter, ◆ Patterns: Wrapper Facade, Builder, Composite, Interpreter, Visitor, Observer, . ◆ Extensibility through new visitors, observers Gustaf Neumann, Uwe Zdun Slide 11 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Partial Design of the XML Parser/Interpreter Visitor Interpreter/Composite Client TreeVisitor AbstractNode XMLParser NodeBuilder Builder XMLVisitor ... XMLNode TclXMLParser XMLBuilder VisitObserver may be Functions used as per-object mixin TclXML PrintObserver Per-Object Wrapper Facade Observer Gustaf Neumann, Uwe Zdun Slide 12 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Assessments ◆ size 73 lines (including two more visitors), ◆ + 22 lines for the Wrapper Facade and 25 lines for the Composite, ◆ Reuseable Composite implementation and reuseable TclXML wrapper, ◆ Changeability and Adaptability through: – dynamics, – introspection, – patterns in hot spots, – interceptors per-object and filter, ◆ Extensibility through new visitors. Gustaf Neumann, Uwe Zdun Slide 13 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Speed Comparison: XOTcl based HTTP Server vs. Apache ¦ Single Processor 466MHz Celeron Dual 200 MHz PPro Server ¦ Single Processor 466MHz Celeron 10MBit Clients 10MBit Clients Local Clients 100 100 100 ¤ ¥ 80 80 ¥ 80 £ ¤ 60 60 ¤ 60 XOTcl Server £ £ 40 40 40 Apache 1.3.6 Seconds Seconds Seconds Ratio (Percent) 20 20 20 0 0 0 −20 −20 −20 ¡ ¡ ¡ 0 10 20 0 10 20 0 10 20 ¢ ¢ Clients ¢ Clients Clients ◆ Basic functionality of HTTP/1.1 in around 250-400 lines of XOTcl code ◆ 1-20 simultanoues client sessions issuing each 76 HTTP requests. Modern CPUs are fast enough to execute even complex applications in ! object-oriented scripting language with sufficient speed. Gustaf Neumann, Uwe Zdun Slide 14 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 Summary and Conclusions ◆ XOTcl provides high-level language constructs for software composition, ◆ tailored for the use with scripting applications: – dynamics, – (read/write) introspection, – flexible glueing of (preexisting) components. ◆ Combination of: scripting, object-orientation, and high-level language constructs Flexible composition of software systems. ) Coping with changes at runtime/design time. ) Gustaf Neumann, Uwe Zdun Slide 15 University of Essen XOTcl– an Object-Oriented Scripting Language June, 2000 More XOTcl Material ◆ Gustaf Neumann, Uwe Zdun: Filters as a Language Support for Design Patterns in Object-Oriented Scripting Languages, Proceedings of the 5th Conference on Object-Oriented Technologies and Systems (COOTS´99), San Diego, May 3-9, 1999. ◆ Gustaf Neumann, Uwe Zdun: Enhancing Object-Based System Composition through Per- Object Mixins, Proceedings of Asia-Pacific Software Engineering Conference (APSEC‘99), Takamatsu, Japan, December 6-10, 1999. ◆ Gustaf Neumann, Uwe Zdun: Towards the Usage of Dynamic Object Aggregations as a Form of Composition, Proceedings of Symposium of Applied Computing (SAC‘00), Como, Italy, March 19-21, 2000. ◆ Gustaf Neumann, Uwe Zdun: High-Level Design and Architecture of an HTTP-Based Infrastructure for Web Applications, Word Wide Web Journal, Baltzer, early 2000. ◆ More on http://www.xotcl.org, http://nestroy.wi-inf.uni-essen.de/xotcl Gustaf Neumann, Uwe Zdun Slide 16 University of Essen.